Evaporator

ABSTRACT

An evaporator ( 10 ) includes a substantially plate-like body member ( 12 ) defining an operatively outer surface ( 14 ) and an operatively inner surface ( 16 ), both surfaces ( 14, 16 ) being substantially smooth to inhibit detritus from attaching to the body member ( 12 ). The body member ( 12 ) is shaped to cause incoming fluid from which heat is to be extracted, in use, to follow an extended, circuitous path past the body member ( 12 ) initially along the outer (surface  14 ) of the body member ( 12 ) prior to the fluid impinging on the inner surface ( 16 ) of the body member ( 12 ).

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority from Australian Provisional Patent Application No 2014903499 filed on 2 Sep. 2014, the contents of which are incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates, generally, to heat exchange between fluids and, more particularly, to an evaporator for use in a heat extraction process and to an evaporator assembly which includes the evaporator. The disclosure extends still further to heat pump circuit which includes the evaporator assembly.

The evaporator of the disclosure is particularly suitable for use in extracting heat energy from waste water, or grey water, of premises but those skilled in the art will readily appreciate that the evaporator is not restricted to use in such an application. Other applications will be readily apparent to a person of ordinary skill in the art. The term “evaporator” is to be understood in a broad sense as a device which extracts heat from an incoming fluid by heating a working fluid of the evaporator. The working fluid of the evaporator may not necessarily vaporise such as would be the case where the working fluid is an anti-freeze/water mixture.

BACKGROUND

Waste water discharged from premises such as a domestic dwelling often contains significant quantities of heat. The term “waste water” is a broad term and includes all waste water from premises including sewage and “grey water”. Grey water generally comes from basins, baths, showers, washing machines, dishwashers, etc. and often contains significant quantities of heat energy. Waste water is normally discharged into the municipal drainage system without extracting what could be a useful source of heat energy. In this specification, the term “waste water” is intended to cover all waste water as well as only grey water.

The Applicant has proposed a system for treating waste water in International Patent Publication No. WO 2011/160185 dated 24 Jun. 2011 and has also proposed a system for extracting heat energy from waste water as described in International Patent Publication No. WO 2012/061891 dated 9 Nov. 2011. Both of these documents are incorporated herein by reference in their entirety.

Waste water has features which render removal of heat via a heat exchange process problematic. It can be corrosive. Further, the waste water often contains stringy particulate material, such as hair, which can become ensnared or entangled in the heat exchanger. Still further, the waste water often contains colloidal material such as fats, oils, detergents and other chemical formulations that serve to cause clumping of waste material which can clog up a heat exchange surface of a heat exchanger. Such clogging reduces the heat exchange capability of the heat exchanger. Still other particulate materials such as sand, lint, etc. are often entrained in the waste water and these particulate materials can also clog up the heat exchange surface of the heat exchanger. In addition, the waste water may also have a high bacterial content which can colonise a surface of a heat exchanger and coat its surface adversely affecting operation of the heat exchanger.

Further, combining waste water treatment with heat recovery can present problems as water enters a collection tank at irregular intervals. Further, water is also discharged from the collection tank periodically either as more water enters the collection tank or at irregular intervals when water is drawn from the tank for treatment. Unlike other waste streams, the formulation of waste water is not controlled and varies greatly from premises to premises and day to day. Any particular volume of waste water can contain any or all of the above listed contaminants with some combinations reinforcing the problematic properties of the individual components.

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each claim of this application.

SUMMARY

Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.

In a first aspect, there is provided an evaporator which includes a substantially plate-like body member defining an operatively outer surface and an operatively inner surface, both surfaces being substantially smooth to inhibit detritus from attaching to the body member and the body member being shaped to cause incoming fluid from which heat is to be extracted, in use, to follow an extended, circuitous path past the body member initially along the outer surface of the body member prior to the fluid impinging on the inner surface of the body member.

By “plate-like” is meant, unless the context clearly indicates otherwise, a thin structure having length and width dimensions substantially greater than a thickest thickness dimension. Further, by “substantially smooth” is meant, unless the context clearly indicates otherwise, that the surfaces of the body member contain no sharp edges or abrupt changes in surface profile.

The body member may comprise a pair of opposed side members interconnected by a bridging portion. At least the bridging portion may be curved so that, when viewed in plan, the body member has a substantially U-shape or horseshoe shape. Further, when viewed in plan, the body member is substantially symmetrical about a centre line, extending substantially in the direction of the side members, bisecting the body member.

The evaporator may include a flow directing member (or diverter) for directing the incoming fluid into contact with the outer surface of the body member at an upstream end of the body member.

The body member may have a pair of spaced ends and the flow directing member may be attachable to either one of the ends of the body member. This improves the versatility of the evaporator and renders it suitable for use in a collection tank with an inlet opening on either side of the tank.

The body member may have a height exceeding a maximum height of a body of the incoming fluid, in use, to inhibit detritus carried in the fluid being ensnared on the body member.

The body member may be formed from a pair of sheets of a heat conductive, corrosive resistant material secured together and defining passages for a working fluid, the passages extending predominantly in a direction of movement of the incoming fluid past the body member. The body member may have an upper edge and a parallel, lower edge and the passages may extend substantially parallel to those edges with only short bridging sections of the passages extending transversely to the edges of the body member.

In a second aspect, there is provided an evaporator which includes

a substantially plate-like body member defining an operatively outer surface and an operatively inner surface and a pair of spaced ends, both surfaces being substantially smooth to inhibit detritus from attaching to the body member, the body member comprising a pair of opposed side members interconnected by a bridging portion, the body member being formed from a pair of sheets of a corrosive resistant material secured together and defining passages for a working fluid, the passages extending predominantly in a direction of movement of the incoming fluid past the body member; and

a flow directing member attached to an end of the body member, the flow directing member directing incoming fluid into contact with the outer surface of the body member at an upstream end of the body member.

The passages of the body member may be formed by blowing a fluid through the body member to inhibit formation of sharp edges or sharp transitions in passage walls of the body member.

The flow directing member may be removably attached to the end of the body member, the flow directing member being configured to be attachable to either end of the body member so that either end of the body member can function as the upstream end in use.

In a third aspect, there is provided an evaporator assembly which includes

a collection tank defining a detention chamber for incoming fluid from which heat is to be extracted;

an evaporator, as described above, received in the detention chamber, the collection tank having an inlet opening and an opposed discharge opening, at least the discharge opening being arranged at a height relative to the evaporator lower than an upper edge of the body member of the evaporator; and

a conduit interconnecting a region of the tank at its operatively lowest point and the discharge opening to inhibit the incoming fluid from overflowing the upper edge of the body member of the evaporator.

The collection tank may define a sump which defines the lowest point of the tank, the body member of the evaporator being arranged about the sump substantially to isolate the sump from the inlet opening of the tank.

At least a part of a floor of the collection tank may be angled to encourage the formation of eddies in the incoming fluid to cause heat exchange by convection as well as by thermal conduction.

The conduit may be a snorkel member removably attachable to the discharge opening.

The snorkel member may ensure that the incoming fluid is inhibited from flowing directly out the discharge opening of the collection tank. In effect, the snorkel member breaks the flow path of the incoming fluid vertically, requiring the incoming fluid to travel down to a bottom of the collection tank before flowing back up to the discharge opening. In other words, the snorkel member inhibits flow of warm incoming fluid directly from the inlet opening to the discharge opening without any extraction of heat energy which would result in substantial loss of heat energy.

Both the collection tank and the evaporator may be symmetrical so that either opening of the collection tank can be used as the inlet opening with the other opening then functioning as the discharge opening.

The body member of the evaporator may have a pair of spaced ends and the assembly may include a flow directing member attachable to either one of the ends of the body member, the flow directing member being arranged adjacent the inlet opening for directing the incoming fluid into heat exchange contact with the outer surface of the body member. Due to the symmetrical nature of the body member and the tank, the flow directing member can be attached to either end, depending on which opening of the collection tank is to be used as the inlet opening.

The disclosure extends to a heat pump which includes an evaporator assembly as described above.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the disclosure are now described by way of example with reference to the accompanying drawings in which:

FIG. 1 shows a schematic, perspective view of an embodiment of an evaporator;

FIG. 2 shows a schematic, front view of the evaporator;

FIG. 3 shows a schematic, plan view of the evaporator;

FIG. 4 shows a schematic, sectional view of the evaporator taken along line IV-IV in FIG. 2 of the drawings;

FIG. 5 shows a schematic, front view of an embodiment of an evaporator assembly;

FIG. 6 shows a schematic, plan view of the evaporator assembly with a lid of a collection tank of the assembly removed to show the location of the evaporator within the collection tank;

FIG. 7 shows a schematic, sectional side view of a collection tank of the evaporator assembly with an evaporator of the assembly omitted;

FIG. 8 shows a schematic, front view of the evaporator assembly indicating the formation of eddies in the incoming fluid;

FIG. 9 shows a schematic, plan view of the evaporator assembly indicating the flow path of an incoming fluid, from which heat is to extracted, relative to the evaporator of the assembly;

FIG. 10 shows a schematic representation of a first embodiment of a heat pump circuit incorporating the evaporator assembly of FIG. 5; and

FIG. 11 shows a schematic representation of a second embodiment of a heat pump circuit incorporating the evaporator assembly of FIG. 5.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In the drawings, reference numeral 10 generally designates an embodiment of an evaporator. The evaporator 10 comprises a substantially plate-like body member 12. As described, by “plate-like” is meant that the body member 12 is a thin structure having length and width dimensions substantially greater than a thickest thickness dimension.

The body member 12 defines an operatively outer surface 14 and an operatively inner surface 16, both surfaces being substantially smooth to inhibit detritus from attaching to the body member 12. It is to be noted that, in FIG. 1 of the drawings, demarcations of the passages in the surface 16 have been omitted for the sake of clarity. In practice, the inner surface 16 has a finish which has the same appearance as that of the outer surface 14.

The body member 12 is shaped to cause incoming fluid from which heat is to be extracted to follow an extended, circuitous path, as shown by arrows 18 in FIG. 9 of the drawings, initially along the outer surface 14 of the body member 12 prior to the fluid impinging on the inner surface 16 of the body member 12 to force the incoming fluid to follow a path past, and in heat exchange contact with, the body member 12.

To form this extended path 18, the body member 12 comprises a pair of opposed side members 20 interconnected by a bridging portion 22. The bridging portion 22 is curved so that, when viewed in plan (FIG. 3), the body member 12 has a substantially U-shape or horseshoe shape.

The body member 12 further defines an operatively lower edge 24 and an operatively upper edge 26 and a pair of spaced ends 28. Each end 28 carries an attachment member 30 in the form of an inwardly directed flange or lip. The body member 12 is symmetrical about a centre line 32 bisecting the body member 12 to improve ease of use and facilitate installation of the evaporator 10 in a collection tank 34 (FIGS. 5 & 6) as will be described in greater detail below.

The evaporator 10 includes a flow directing member, or diverter, 36 which is attachable, via the attachment flange 30 to that end 28 of the body member 12 which, in use, will be adjacent an inlet opening 38 (FIGS. 5-7) of the collection tank 34. The diverter 36 serves to direct the incoming fluid into contact with the outer surface 14 of the inlet side member 20 of the body member 12 of the evaporator 10. The diverter 36 further serves to reduce the impact of the incoming fluid on the body member 12 of the evaporator 10.

The body member 12 is formed from two sheets 40 (FIG. 4) of a corrosion resistant material, such as stainless steel or other similar material, which are welded together at spaced intervals to form seams 42 defining passages 44. When fabricating the body member 12, the sheets 40 are forced apart, for example, by forcing fluid such as air between the sheets 40 to form passages 42 through which working fluid circulates to effect heat exchange with the incoming fluid impinging on the surfaces 14, 16 of the body member 12 of the evaporator 10.

With this construction of the body member 12, the surfaces 14, 16 of the body member 12 are substantially smooth, as defined. This has the benefit that detritus entrained in the incoming fluid is much less likely to be trapped in or on the body member 12 and this reduces the likelihood of the body member 12 being clogged by such detritus.

In this regard, it is also to be noted that the body member 12 has a height dimension ‘h’, as measured between the edges 24, 26 of the body member 12, which exceeds the distance between the inlet opening 38 of the collection tank 34 and a floor 46 of the collection tank 34, on which the evaporator 10 is seated or positioned, in use. Where the incoming fluid is waste water, it often contains stringy material, such as human or animal hair or fibres from clothing etc. By having the operatively upper edge 26 of the body member 12 above the height of the inlet opening 38 of the collection tank 34, and with the substantially smooth surfaces 14, 16 of the body member 12, the likelihood of this stringy material attaching to the evaporator is minimised.

The evaporator 10 includes a pair of working fluid conduits 48 in communication with the passages 44 defined in the body member 12. One of the conduits 48 functions as a working fluid inlet conduit with the other conduit functioning as a working fluid outlet conduit. It will be appreciated that, due to the symmetry of the body member 12 of the evaporator 10 about the centre line 32, either one of the conduits 48 can be selected as the inlet conduit, with the other conduit 48 then functioning as the outlet conduit, depending on the side of the body member 12 to which the diverter 36 is attached.

Referring now in greater detail to FIGS. 5-7 of the drawings, an embodiment of an evaporator assembly is illustrated and is designated generally by the reference numeral 50.

The assembly 50 comprises the collection tank 34 which defines a detention chamber 52 into which the incoming fluid is charged to extract heat energy from the working fluid as will be described in greater detail below. The evaporator 10, as described above with reference to FIGS. 1-4 of the drawings, is received in the detention chamber 52 of the collection tank 34 and seats on the floor 46 of the collection tank 34.

The collection tank 34 has a side wall 54 circumscribing the floor 46 of the collection tank 34. The side wall 54 defines the inlet opening 38 and an opposed discharge opening 55, at the same height in the side wall 54 as the inlet opening 38. It is to be noted that, like the evaporator 10, the collection tank is symmetrical about a centre line 56 (FIG. 6) bisecting the collection tank 34. Thus, in use, either opening 38, 55 can be used as the inlet opening with the other opening 38, 55 then being used as the discharge opening. This facilitates ease of installation of the assembly 50, in use, with minimum disruption or modification required to existing plumbing of premises in which the assembly is being installed.

The selection of which of the openings 38, 55 is to be used as the inlet opening is, of course, subject to the proviso that the diverter 36 of the evaporator must be attached to that end 28 of the side 20 of the body member 12 that will be adjacent the opening 38, 55 selected as the inlet opening 38.

The side wall 54 further defines an access aperture 60 (FIG. 6) to enable access to be gained to the detention chamber 52 of the collection tank 34. This enables the evaporator 10 to be inserted into the detention chamber 52 together with any other ancillary equipment (not shown) that may be required. The access aperture is surrounded by a collar 62 to which a lid (not shown) is attached to seal the detention chamber 52 of the collection tank 34 against ingress of foreign matter.

A rear portion 64 of the collar 62 defines a flat region 66 extending into the detention chamber 52 of the collection tank 34. A channel or groove 68 is defined along each side of the flat region 66. One of these channels 68 acts as a receiving formation for the diverter 36 of the evaporator 10 as shown most clearly in FIG. 6 of the drawings.

The floor 46 of the collection tank 34 defines a substantially flat region 69. A connecting portion 70 of the floor 46, between the flat region 69 and the side wall 54, is angled upwardly from the substantially flat region 69 towards the side wall 54 of the collection tank 34. The angled connecting portion 70 facilitates the formation of eddy currents 72 (FIG. 8). These eddy currents 72 aid in convective heat exchange between the incoming fluid and the evaporator 10 as the incoming fluid flows past the evaporator 10.

Further, the floor 46 of the collection tank 34 defines a sump 74 which, in use, projects below the substantially flat region 69 of the floor 46. A flow conduit, in the form of a snorkel, 76 (FIG. 7) interconnects the sump 74 and the discharge opening 55 of the collection tank 34 as shown most clearly in FIG. 7 of the drawings. It is to be noted that an inlet opening 78 of the snorkel 76, which permits the ingress of fluid into the snorkel 76, is spaced from an inner surface of the sump 74. This enables fluid to enter the snorkel 76 to be discharged through the discharge opening 55 of the collection tank 34. The provision of the snorkel 76 ensures that the level of fluid within the collection tank 34 at any time is maintained at a level 80 (FIG. 5) which is below the height of the upper edge 26 of the evaporator 10. This further serves to inhibit the ensnaring of stringy material on the body member 12 of the evaporator 10.

Referring now to FIG. 10 of the drawings, a first embodiment of a heat pump circuit is illustrated and is designated generally by the reference numeral 90. The heat pump circuit 90 comprises the evaporator assembly 50 with the evaporator 10 mounted in the collection tank 34.

The circuit 90 includes a condenser 92 arranged in a storage tank 94. The working fluid conduits 48 of the evaporator 10 are plumbed into the circuit 90 via thermally insulated piping 96 and 98. Heated, vaporised working fluid is discharged via the conduit 48.1 (FIG. 10) into the pipe 98 where it is fed through a compressor 100 prior to being charged into the condenser 92. Compressed, liquefied working fluid output from the condenser 92 is fed through the pipe 96 via an expansion valve 102 into the working fluid conduit 48.2 of the evaporator 10. The expansion valve 102 is a capillary tube or similar device.

In the embodiment shown in FIG. 10 of the drawings, the refrigerant used is a hydrofluorocarbon (HFC) refrigerant, either a single component HFC refrigerant or a blend of HFC refrigerants. A non-exhaustive list of refrigerants which can be used include R134a, R410a and R417a refrigerants. Those skilled in the art will, however, appreciate that any other suitable refrigerants could be used in the circuit 90.

In FIG. 11 of the drawings, a second embodiment of a heat pump circuit 90 is illustrated. With reference to FIG. 10 of the drawings, like reference numerals refer to like parts, unless otherwise specified.

In this embodiment, the heat pump circuit 90 includes a primary loop heat exchange circuit 104 and a secondary loop heat exchange circuit 106. The primary loop heat exchange circuit 104 contains the condenser 92, the storage tank 94 the compressor 100 and the expansion valve 102. However, instead of the evaporator assembly 50 being plumbed into this circuit 104, the evaporator assembly 50 is plumbed into the secondary loop heat exchange circuit 106.

The primary loop heat exchange circuit 104 and the secondary loop heat exchange circuit 106 exchange energy via a supplementary heat exchanger, illustrated schematically at 108 in FIG. 11 of the drawings.

The secondary loop heat exchange circuit 106 uses an anti-freeze/water mixture as the working fluid. Typically, this mixture comprises approximately 20%-30% by volume of a glycol anti-freeze and water but in some circumstances the glycol content of the mixture could be as high as 80%. Thus the glycol could be present in any one of the following ranges by volume: 10%-20%, 20%-30%, 30%-40%, 40%-50%, 50%-60%, 60%-70%, 70%-80% or 80%-90%. In an embodiment, the glycol comprises about 30% of the mixture. The mixture is circulated through the secondary loop heat exchange circuit 106 by a recirculation pump 110.

The primary loop heat exchange circuit 104 makes use of a conventional refrigerant such as those described above with reference to FIG. 10 of the drawings. The heated working fluid discharged from the evaporator 10 exchanges heat energy with the refrigerant of the primary loop heat exchange circuit 104 via the supplementary heat exchanger 108.

An advantage of this embodiment is that if a heat pump circuit, such as that represented by the primary loop heat exchange circuit 104, is already present in the premises, minimal modification of that heat exchange circuit 104 is required when the evaporator assembly 50 is installed.

In use, the collection tank 34 of the evaporator assembly 50 is provided with a connecting pipe (not shown) interconnecting the inlet opening 38 and the discharge opening 55 of the collection tank 34. Thus, the collection tank 34 can be plumbed into the conventional plumbing conduits of premises until it is required for use in treating waste water and/or extracting heat from the waste water discharged from the premises.

When it is desired to install the evaporator 10 in the collection tank 34, the connecting pipe is removed. The evaporator 10 is mounted in the detention chamber 52 of the collection tank 34 with the diverter 36 mounted on the body member 12 of the evaporator 10 on that side 20 of the body member 12 in proximity to the inlet opening 38 of the collection tank 34.

The snorkel 76 is connected to the discharge opening 55 of the collection tank 34. The conduits 48 of the evaporator 10 are plumbed into the heat pump circuit 90.

When waste water is released or discharged from the premises, the waste water is charged into the detention chamber 52 of the collection tank 34. Often, this waste water is at an elevated temperature and heat can be extracted from it. The heated waste water is diverted by the diverter 36 of the evaporator 10 into heat exchange contact with the outer surface 14 of the body member 12 of the evaporator 10. Heat exchange between the incoming waste water and the working fluid contained in the evaporator 10 takes place primarily by conduction.

However, the angled portion 70 of the floor 46 of the collection tank 34 encourages formation of the eddies 72 in the waste water. As heat is extracted from the waste water, it sinks towards the floor 46 of the detention chamber 52 causing warmer waste water to rise and to be brought into contact with the outer surface 14 of the body member 12 of the evaporator 10.

The waste water follows the circuitous path shown by arrows 18 in FIG. 9 of the drawings along the outer surface of the body member 12 of the evaporator 10 until the waste water passes the downstream end 28 of the body member 12 of the evaporator 10 (i.e. the end 28 without the diverter 36). Once past this downstream end 28 of the body member 12, the waste water impinges on the inner surface 16 of the body member 12 of the evaporator 10 where further heat extraction from the waste water occurs.

Once the waste water is on that side of the detention chamber 52 where the waste water is in contact with the inner surface 16 of the body member 12 of the evaporator 10, the cooling waste water sinks into the sump 74 of the collection tank 34 where it is drawn into the snorkel 76 to be discharged through the discharge opening 55 of the collection tank 34.

From the discharge opening 55, the waste water can either be further treated as described in the Applicant's above-referenced International Patent Publication No. WO 2011/160185. Instead, the waste water can be discharged via the discharge opening 55 into the drainage system associated with the premises.

The heated or vaporised working fluid from the evaporator 10 is fed through the heat pump circuit 90 to the condenser 92 where heat is extracted from the working fluid to heat water for the premises stored in the hot water storage tank 94. If necessary, the hot water in the storage tank 94 can be further heated by a supplementary heating source (not shown).

It is therefore an advantage of the described embodiments that an evaporator 10 for use in a heat pump circuit 90 is disclosed which lends itself for use in circumstances where heat is to be extracted from waste water. The construction of the evaporator 10 renders it suitable for such a use since the absence of sharp edges or abrupt changes in profile of the surfaces of the evaporator 10 reduce the risk of foreign material, in particular, stringy, particulate or granular material, clogging up the evaporator 10 and, in so doing, reducing its heat exchanger efficiency.

Further, the construction of the evaporator assembly 50, in particular, the symmetry of the body member 12 of the evaporator 10 and the symmetry of the collection tank 34 improve the versatility of the assembly 50 and simplifies the installation of the assembly 50 in the premises.

Still further, the use of the heat pump circuit 90 of FIG. 11 of the drawings also simplifies installation of the evaporator assembly 50 where the assembly 50 is to be plumbed into premises already having a heat pump arrangement requiring minimum modification of the existing heat pump arrangement.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive. 

1. An evaporator which includes a substantially plate-like body member defining an operatively outer surface and an operatively inner surface, both surfaces being substantially smooth to inhibit detritus from attaching to the body member and the body member being shaped to cause incoming fluid from which heat is to be extracted, in use, to follow an extended, circuitous path past the body member initially along the outer surface of the body member prior to the fluid impinging on the inner surface of the body member.
 2. The evaporator of claim 1 in which the body member comprises a pair of opposed side members interconnected by a bridging portion.
 3. The evaporator of claim 2 in which at least the bridging portion is curved so that, when viewed in plan, the body member has a substantially U-shape or horseshoe shape.
 4. The evaporator of claim 2 in which, when viewed in plan, the body member is substantially symmetrical about a centre line, extending substantially in the direction of the side members, bisecting the body member.
 5. The evaporator of claim 1 which includes a flow directing member for directing the incoming fluid into contact with the outer surface of the body member at an upstream end of the body member.
 6. The evaporator of claim 5 in which the body member has a pair of spaced ends and in which the flow directing member is attachable to either one of the ends of the body member.
 7. The evaporator of claim 1 in which the body member has a height exceeding a maximum height of a body of the incoming fluid, in use, to inhibit detritus carried in the fluid being ensnared on the body member.
 8. The evaporator of claim 1 in which the body member is formed from a pair of sheets of a corrosive resistant material secured together and defining passages for a working fluid, the passages extending predominantly in a direction of movement of the incoming fluid past the body member.
 9. An evaporator which includes a substantially plate-like body member defining an operatively outer surface and an operatively inner surface and a pair of spaced ends, both surfaces being substantially smooth to inhibit detritus from attaching to the body member, the body member comprising a pair of opposed side members interconnected by a bridging portion, the body member being formed from a pair of sheets of a corrosive resistant material secured together and defining passages for a working fluid, the passages extending predominantly in a direction of movement of the incoming fluid past the body member; and a flow directing member attached to an end of the body member, the flow directing member directing incoming fluid into contact with the outer surface of the body member at an upstream end of the body member.
 10. The evaporator of claim 9 in which the passages of the body member are formed by blowing a fluid through the body member to inhibit formation of sharp edges or sharp transitions in passage walls of the body member.
 11. The evaporator of claim 9 in which the flow directing member is removably attached to the end of the body member, the flow directing member being configured to be attachable to either end of the body member so that either end of the body member can function as the upstream end in use,
 12. An evaporator assembly which includes a collection tank defining a detention chamber for incoming fluid from which heat is to be extracted; an evaporator, as claimed in claim 1, received in the detention chamber, the collection tank having an inlet opening and an opposed discharge opening, at least the discharge opening being arranged at a height relative to the evaporator lower than an upper edge of the body member of the evaporator; and a conduit interconnecting a region of the tank at its operatively lowest point and the discharge opening to inhibit the incoming fluid from overflowing the upper edge of the body member of the evaporator.
 13. The assembly of claim 12 in which the collection tank defines a sump which defines the lowest point of the tank, the body member of the evaporator being arranged about the sump substantially to isolate the sump from the inlet opening of the tank.
 14. The assembly of claim 12 in which at least a part of a floor of the collection tank is angled to encourage the formation of eddies in the incoming fluid to cause heat exchange by convection as well as by thermal conduction.
 15. The assembly of claim 12 in which the conduit is a snorkel member removably attachable to the discharge opening.
 16. The assembly of claim 12 in which both the collection tank and the evaporator are symmetrical so that either opening of the collection tank can be used as the inlet opening with the other opening then functioning as the discharge opening.
 17. The assembly of claim 12 in which the body member of the evaporator has a pair of spaced ends and in which the assembly includes a flow directing member attachable to either one of the ends of the body member, the flow directing member being arranged adjacent the inlet opening for directing the incoming fluid into heat exchange contact with the outer surface of the body member.
 18. (canceled)
 19. An evaporator assembly which includes a collection tank defining a detention chamber for incoming fluid from which heat is to be extracted; an evaporator, as claimed in claim 9, received in the detention chamber, the collection tank having an inlet opening and an opposed discharge opening, at least the discharge opening being arranged at a height relative to the evaporator lower than an upper edge of the body member of the evaporator; and a conduit interconnecting a region of the tank at its operatively lowest point and the discharge opening to inhibit the incoming fluid from overflowing the upper edge of the body member of the evaporator. 